You can also try if it would help to remove the heart rate sensor off your chest, detach the connector from the strap, wait for 30 seconds, replace the connector, put the heart rate sensor back onto your chest, and check if then your heart rate is found.

If you have tried everything above and you still get 'Check WearLink!/ Check heart rate transmitter!' message, the heart rate sensor battery may be empty. For further information, see here.